1. Field of the Invention
This invention relates generally to temperature sensors, and particularly to determining various temperature points using a reduced voltage.
2. Description of Related Art
In modern high frequency integrated circuits, operating temperature has become increasingly important. Power consumption and device temperatures may generally be related to clock frequency and the number of nodes on a semiconductor device toggling at these high frequencies. The increased toggling frequencies generate additional heat, which may cause a semiconductor device to reach very high temperatures. Generally, devices are specified to operate in a certain temperature range within which the device has been characterized. Temperature sensors on these devices may be useful to control the operational parameters of the device. For example, if the temperature of the device rises above a temperature threshold, operation of the device may be modified to reduce heat generation until the temperature of the device falls below a temperature threshold. Once the lower temperature threshold is met, the operating parameters may be returned to their previous values. A variety of operating parameters may be modified to reduce the temperature. For example, a device may reduce its clock rate for all or portions of the device, or it may implement low power modes of various analog circuits to reduce heat generation. Other examples include reducing the refresh rate of Dynamic Random Access Memory (DRAM) and adjusting the impedance of output devices. Additionally, the device may report its current temperature to other devices in a system for overall system temperature monitoring and control.
Many circuit devices such as resistors, diodes, and transistors have operating characteristics that vary as temperature varies. These characteristics may be used to sense ambient temperature near these devices. Many different configurations of temperature sensors may be devised to take advantage of these characteristics.
Some temperature sensors take advantage of these varying characteristics by applying a voltage across a resistor or a diode. The resulting analog voltage may then be sampled using an analog-to-digital converter to arrive at a temperature estimate. However, these types of sensors may be complex and not be able to sense temperatures over a wide range.
Other temperature sensors may use two similar current sources to generate a current flowing through a diode and a current flowing through a resistor. The respective voltage drops produced by the current flowing through the diode and the current flowing through the resistor are compared in order to determine whether the present temperature is above or below a certain temperature. However, there may be a need for defining a variety of temperature points.
As a result, there is a need for a temperature sensor that can operate at lower voltages while allowing a variety of temperature sensing thresholds for communication to other devices on a semiconductor device or within a system.